Abbreviation: RAPD
The presence of a unilateral afferent pupillary defect. If a flashlight is swung back and forth between the two eyes (swinging flashlight test), the eye with the afferent pupillary defect appears to dilate in response to illumination. This happens because the pupil constricts in response to illumination of the contralateral eye (an intact indirect pupillary reflex) but fails to constrict with illumination of the affected eye (impaired direct pupillary reflex). This phenomenon does not occur with bilateral afferent pupillary defects.